System and method for automatically controlling vehicle speed to desired cruise speed

Abstract

A system and method for automatically controlling a vehicle speed to a desired cruise speed are disclosed in which when the vehicle speed is reduced by a first predetermined value from a set and stored cruise speed at which the vehicle is cruising during the operation of the automatic cruise control, the gear range of a vehicular transmission is shifted down and simultaneously the set and stored cruise speed is updated to reduce the set and stored cruise speed by a second predetermined value so that the vehicle speed coincides with the updated cruise speed. In addition, after a predetermined time has elapsed, the gear range is shifted up and the updated cruise speed is returned to the original cruise speed.

What is claimed is: 
     
       1. A system for automatically controlling speed of a vehicle to a desired cruise speed, comprising: (a) first means for detecting current speed of the vehicle;   (b) second means for deriving a set command for a desired cruise speed for the vehicle;   (c) third means responsive to the set command derived from the second means and the detected current speed derived from the first means for: (i) storing the desired cruise speed,   (ii) deriving an indication of a speed difference between the current vehicle speed and the desired cruise speed, and   (iii) adjusting an operating variable of an engine driving force adjusting mechanism for the vehicle on the basis of the derived speed difference indication so that the current vehicle speed substantially coincides with the stored cruise speed;     (d) fourth means for deriving an indication of whether the current vehicle speed is less than the desired cruise speed by at least a first predetermined value;   (e) fifth means for selectively shifting down a transmission mechanism of the vehicle in response to the indication derived by the fourth means; and   (f) sixth means for updating the stored cruise speed to reduce the desired cruise speed by a second predetermined value which prevents an abrupt torque increase of the vehicle engine in response to the indication derived by the fourth means.   
     
     
       2. The system of claim 1 further comprising seventh means for: (i) deriving an indication of the occurrence time of the shift down performed by the fifth means, and   (ii) determining whether a predetermined time has elapsed since the occurrence time of the shift down, and eighth means for shifting up the transmission mechanism in response to the predetermined time elapsing.   
     
     
       3. The system of claim 2 further comprising ninth means for returning the updated cruise speed to the originally stored cruise speed and shifting up the transmission means in synchronization with the eighth means. 
     
     
       4. The system of claim 3, wherein the seventh means deenergizes an overdrive cancelling solenoid to activate the transmission into the overdrive mode. 
     
     
       5. The system of claim 4, wherein the transmission mechanism is an automatic transmission. 
     
     
       6. The system of claim 5, wherein the fifth means shifts down from a fourth speed overdrive range of the automatic transmission to a third range. 
     
     
       7. The system of claim 6, wherein the fifth means includes an overdrive cancelling solenoid for cancelling the overdrive mode by energization of the fourth means. 
     
     
       8. The system of claim 1, wherein the first predetermined value is 6 Km/h and second predetermined value is 4.5 Km/h. 
     
     
       9. The system of claim 1, wherein the engine driving force adjusting mechanism includes an engine throttle valve and the operating variable includes an opening angle of the throttle valve. 
     
     
       10. A method of automatically controlling speed of a vehicle to a desired cruise speed, comprising the steps of: (a) detecting current vehicle speed;   (b) storing an indication of desired cruise speed for the vehicle;   (c) deriving an indication of the difference between the detected current vehicle speed and the indication of stored cruise speed;   (d) adjusting an operating variable of a driving force adjusting mechanism of an engine of the vehicle in response to the indication of the speed difference so that the vehicle speed substantially coincides with the stored cruise speed;   (e) determining whether the detected current vehicle speed is less than the stored cruise speed by a first predetermined value;   (f) shifting down a transmission mechanism of the vehicle when the detected vehicle speed is less than the stored cruise speed by the first predetermined value and simultaneously updating the stored cruise speed to reduce the stored cruise speed by a second predetermined value; and   (g) adjusting the vehicle speed so that it substantially coincides with the updated cruise speed.